In a large package delivery system, millions of packages picked up from thousands of locations over a large geographical area must be transported, primarily by truck and airplane, to a correspondingly large number of destinations that are also scattered over a large area. Such delivery services are offered within guaranteed times as short as one day. To meet a rigorous schedule and provide accurate deliveries, a package delivery company must use automated transfer systems to match incoming packages with proper transport that is heading to their destinations.
Belt and roller conveyor systems have often been used in package sorting systems to move packages from incoming loading docks to outgoing transport. Typically, conveyors carry packages unloaded from a truck to a worker who manually sorts them by reading address information on shipping labels attached to the packages. The worker then places the packages onto receiving conveyors or chutes which carry the packages either to a loading dock for loading onto outgoing trucks, or to another sorting station for a narrower breakdown of destinations. A distribution hub in a package delivery system may have as many as 20 to 60 sorting stations operating simultaneously. By providing vertically stacked rows of receiving conveyors, the sorting operation could be accommodated in a relatively small amount of floor space.
To automate handling of articles in conveyor systems, conveyor diverter assemblies have been developed. Examples of conveyor diverters are shown in U.S. Pat. Nos. 4,798,275 to Leemkuil et. al., and 4,174,774 to Bourgeois, both of which are incorporated herein by reference. However, such diverters are used primarily to divert articles from a main linear conveyor. Thus, such systems occupy a relatively large amount of space. This problem is overcome by the rotary sorter system shown in U.S. Pat. No. 5,284,252 to Bonnet, assigned to the assignee of the present application. In this system, destination codes on shipping label of packages are machine read, and the packages are transferred onto powered conveyor modules mounted on a rotating distribution assembly. The individual module is then rotated and elevated or lowered into alignment with one of a plurality of destination conveyors that are spaced apart both horizontally and vertically. After such alignment, the modules rollers are operated to discharge the package onto the destination conveyor. In the Bonnet system, packages can be rapidly sorted without human intervention by an apparatus that occupies a small amount of floor space.
For some circumstances, it would be advantageous to have a compact package sorting system that did not require moving a conveyor module holding a package from a loading point to a discharge point.